A work-piece carrying robot or wafer transfer robot is typically incorporated in a producing system for a semiconductor device. Such a producing system includes a plurality of chambers for processing under a reduced pressure atmosphere. The work-piece carrying robot is operated such that a semiconductor wafer is put in and out of a specified chamber among a plurality of the chambers. In this case, when the specified chamber is returned to a normal pressure state each time a semiconductor wafer is carried in and out of the chamber, much time is required to depressurize the chamber again and start processing, which cause decreased throughput. Therefore, in recent years, a producing system has been commonly employed in which a space including a work-piece carrying robot for carrying-in/carrying-out a semiconductor wafer to and from respective chambers is set to be a preliminary depressurized chamber (referred to as a load lock chamber). According to the producing system described above, a semiconductor wafer can be carried-in/carried-out without returning the inside of the chamber to a normal pressure state and thus the throughput is increased.
Various work-piece carrying robots aiming to improve a carrying efficiency and to shorten an operating time have been proposed as a work-piece carrying robot which is used in the above-mentioned producing system. For example, in Japanese Patent Laid-Open No. Hei 7-142551, a carrier arm device is proposed which includes a first arm part which is supported turnably, a second arm part which is turnably supported at a tip end of the first arm part, and a third arm part whose center portion is turnably supported at a tip end of the second arm part. A work-piece placing part for being placed and holding a work-piece is formed at both ends of the third arm part so that two work-pieces can be handled at a time.
Further, for example, in Japanese Patent Laid-Open No. Hei 11-226883, a carrier robot is proposed in which limitation of an arm turning quantity is improved to enhance throughput. In this carrier robot, a moving member is provided which reciprocates over a specified range corresponding to rotation of a shaft by a drive source and the moving range of the moving member is restricted by a sensor part in order to restrict a turning range of the moving member. In this carrier robot, a sensor is arranged so as to be capable of corresponding to a rotational angle of 360 degrees or more of the shaft and thus this patent reference describes that the moving member can be accessed in either direction.
In the carrier arm device as described in the former patent reference, motors are respectively connected to three drive shafts which are a turning shaft, an expansion-contraction shaft, and a third arm turning shaft. However, no turning controls for the respective drive shafts are described in this reference, and it is conceived that a stepping motor is provably used to enhance a turning accuracy. In this case, reduction gear ratio cannot be increased and cost for the device increases.
Further, in the carrier robot described in the latter patent reference, a turning quantity of its arm is improved but unlimited turning is not possible and the turning quantity is limited by a length of a spiral-shaped groove that is formed on a cam member. Accordingly, when turning is performed as restricted in one direction like an operation in the load lock chamber, the arm is required to be turned reversely once per several times and thus a time loss occurs and throughput is not improved.